Photosensitive film for circuit formation and process for producing printed wiring board

ABSTRACT

The photosensitive film for circuit formation of the present invention has: on a first film (base film), a photosensitive layer having a thickness of 0.1 to 10 μm; or a photosensitive layer having a thickness of 0.1 to 14 μm and containing a 2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane.

This is a National Phase Application in the United States ofInternational Patent Application No. PCT/JP02/03211 filed Mar. 29, 2002,which claims priority on Japanese Patent Application No. 2001-096138,filed Mar. 29, 2001. The entire disclosures of the above patentapplications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a photosensitive film for circuitformation and a process for producing a printed wiring board.

BACKGROUND ART

In producing a printed wiring board, a photosensitive film for circuitformation is used to form a resist film for plating or etching. The filmis formed by applying a photosensitive resin composition on a first film(base film), drying the applied composition so as to form aphotosensitive layer, and then laminating a second film (protectivefilm) on the photosensitive layer. Then, the first film and thephotosensitive layer as transfer layers have heretofore been laminatedonto a substrate to be laminated of a printed wiring board.

To laminate the conventional photosensitive film for circuit formation,the second film is removed first, and then the transfer layer is placedon the substrate such that the photosensitive layer faces the substrate.Thereafter, a heating roller is pressed against the first film so as tocrimp the transfer layer, in other words, the first film and thephotosensitive layer, on the substrate.

To expose the photosensitive layer to light, a negative mask is placedon the first film, and the photosensitive layer is irradiated with a rayof light for exposure through the negative mask. Then, when thephotosensitive layer is developed after removal of the negative mask andsubsequent removal of the first film, the same pattern as that of thenegative mask is obtained on the photosensitive layer. With thephotosensitive layer remaining on the substrate as a resist film, asubsequent plating or etching step is carried out.

As the first film, a film (such as a polyethylene terephthalate (PET)film) having a 5% elongation load per unit width (in a longitudinaldirection) at 80° C. of not lighter than 100 g/mm is used. Its thicknessis generally about 20 μm. The first film must have such a thickness soas to increase the tensile strength of the photosensitive film forcircuit formation. Further, the film must have hardness to some extent.

The photosensitive layer is constituted by a photosensitive materialcharacterized in that when irradiated with ultraviolet radiation or thelike, physical properties of irradiated portions change. As thephotosensitive material, a suitable composition is selected according toapplication purposes. The thickness of the photosensitive layer is setat, for example, 25, 33, 40 or 50 μm, according to needs.

The second film is a protective film which may comprise a polyethyleneand have a thickness of, for example, 30 μm.

The transfer layer must conform to pits and projections on the substratewhen laminated so as to avoid occurrence of non-crimped portions betweenthe photosensitive layer and the substrate.

In recent years, an increase in density of wiring of a printed wiringboard is underway, and high resolution is demanded. To achieve highresolution of the photosensitive film for circuit formation, it iseffective to decrease the thickness of the photosensitive layer.However, since the amount of the photosensitive layer to conform to pitsand projections on the surface of the substrate is decreased, theconventional photosensitive film for circuit formation has manynon-crimped portions between the substrate and the transfer layer.Therefore it cause a problem that a satisfactory yield cannot beobtained. Further, since the first film in the conventionalphotosensitive film for circuit formation must have the foregoingthickness and hardness, the flexibility of the whole transfer layer isinsufficient. Therefore, it is difficult for the transfer layer toconform to pits and projections on the surface of the substrate in orderto laminate completely. As a result, many non-crimped portions occurbetween the substrate and the transfer layer, causing a problem that asatisfactory yield cannot be obtained.

To overcome these problems, a variety of methods have heretofore beenproposed. For example, there is a method in which the photosensitivefilm for circuit formation is laminated on the substrate after water isapplied to the substrate (See Japanese Patent Application Laid-Open Nos.1982-21890 and 1982-21891).

In this method, since a thin water layer is applied uniformly, thesurface of the substrate must be cleaned. Further, when a small-diameterthrough hole is present, water collected in the through hole is liableto cause a reaction with the photosensitive layer, causing a problemsuch as a reduction in developability.

Further, there is also proposed a method in which the photosensitivefilm for circuit formation is laminated on the substrate after a liquidresin is laminated on the substrate so as to form an adhesiveintermediate layer (See Japanese Patent Application Laid-OpenNo.1977-154363).

This method has problems such as reductions in developability andremovability with respect to a small-diameter through hole and anincrease in costs caused by application of the liquid resin.

In addition, there is also known a method by which lamination is carriedout under a reduced pressure by use of a vacuum laminator (See JapanesePatent Publication No. 1978-31670 and Japanese Patent ApplicationLaid-Open No. 1976-63702).

This method is rarely used in general circuit formation since itrequires an expensive device and it takes time to produce a vacuum. Themethod is used only for lamination of a permanent mask used afterformation of a conductor. In the lamination of the permanent mask aswell, a further improvement in conformance to the conductor is desired.

As described above, a photosensitive film for circuit formation whichhas excellent conformance to a conductor and conforms to an increase indensity of wiring of a printed wiring board has heretofore been desired.

DISCLOSURE OF THE INVENTION

The present invention provides a photosensitive film for circuitformation which has a photosensitive layer having a thickness of 0.1 to10 μm on a first film (base film).

Further, the present invention also provides a photosensitive film forcircuit formation which has a photosensitive layer having a thickness of0.1 to 14 μm and containing a2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane on a first film.Preferably, the photosensitive layer contains (A) a binder polymer, (B)a photopolymerizable compound having at least one polymerizableethylenically unsaturated bond, and (C) a photopolymerization initiator.

The binder polymer (A) is preferably a polymer containing methacrylicacid as a copolymerizable component. The binder polymer (A) has an acidvalue of preferably 100 to 500 mgKOH/g. The binder polymer (A) has aweight average molecular weight of preferably 20,000 to 300,000. Thebinder polymer (A) preferably contains styrene or a styrene derivativeas a copolymerizable component. The content of styrene or the styrenederivative is preferably 0.1 to 30 wt % of all copolymerizablecomponents.

The photopolymerizable compound (B) preferably contains a2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane.

The 2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane is notnecessarily required when the photosensitive layer has a thickness of0.1 to 10 μm. However, it is preferable to use the2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane alone or in acombination with other photopolymerizable compounds as the component (B)of the photosensitive layer, when the thickness of the photosensitivelayer is 0.1 to 10 μm or 0.1 to 14 μm.

Further, the 2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane ispreferably represented by the following general formula (I):

(wherein R¹ and R² each independently represent a hydrogen atom or amethyl group, X¹ and X² each independently represent an alkylene grouphaving 2 to 6 carbon atoms, and p and q are positive integers selectedsuch that p+q=4 to 40.) Of these, X¹ and X² are preferably an ethylenegroup or a propylene group, and are particularly preferably an ethylenegroup.

Further, the photosensitive film for circuit formation of the presentinvention preferably has a cushion layer between the first film and thephotosensitive layer, and the cushion layer preferably has higherinterlayer adhesion to the first film than to the photosensitive layer.The cushion layer is preferably composed mainly of a copolymercontaining ethylene as a copolymerizable component. The copolymer ispreferably an EVA (ethylene/vinyl acetate copolymer) containing 60 to 90wt % of copolymerized ethylene or an EEA (ethylene/ethyl acrylatecopolymer) containing 60 to 90 wt % of copolymerized ethylene. Thethickness of the cushion layer is preferably 1 to 100 μm.

Further, the photosensitive film for circuit formation of the presentinvention preferably has a second film (protective film) on the oppositeside of a side of the photosensitive layer on which the first film (basefilm) is present. The second film preferably has lower adhesion to thephotosensitive layer than adhesion between the cushion layer and thephotosensitive layer.

The present invention also provides a method for producing a printedwiring board using the foregoing photosensitive film for circuitformation.

This method comprises the steps of laminating the foregoingphotosensitive film for circuit formation on a substrate while peelingthe second film (protective film) such that the photosensitive layermakes contact with the substrate, exposing the laminated film to light,then removing the first film (base film) or cushion layer which is inintimate contact with the photosensitive layer from the photosensitivelayer, and then developing the photosensitive layer.

Further, another method comprises the steps of laminating the foregoingphotosensitive film for circuit formation having the second film on asubstrate while peeling the second film (protective film) such that thephotosensitive layer makes contact with the substrate, removing thefirst film (base film) or cushion layer which is in intimate contactwith the photosensitive layer from the photosensitive layer, exposingthe photosensitive layer to light, and then developing thephotosensitive layer.

The present specification relates to a subject matter contained inJapanese Patent Application No. 2001-96138, filed on Mar. 29, 2001. Thedisclosure of which is expressly incorporated herein by reference in itsentirety.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

In the present invention, (meth)acrylic acids refer to acrylic acid andcorresponding methacrylic acid, (meth)acrylates refer to acrylates andcorresponding methacrylates, and (meth)acryloyl groups refer to anacryloyl group and a corresponding methacryloyl group.

A photosensitive film for circuit formation of the present invention maytake a two-layer structure in which a photosensitive layer is formed ona first film, a three-layer structure in which a cushion layer is formedbetween a first film and a photosensitive layer, a three-layer structurein which a second film (protective film) is formed on a photosensitivelayer formed on a first film, or a four-layer structure in which acushion layer and a photosensitive layer are formed on a first film anda second film (protective film) is further formed on the photosensitivelayer.

The first film in the present invention is used as a base film. A filmwhich can be used as the first film is not particularly limited. Thefirst film preferably has a film thickness of 2 to 100 μm, morepreferably 5 to 20 μm, and particularly preferably 8 to 16 μm. When thethickness is smaller than 2 μm, the first film may be torn when peeled,while when it is larger than 100 μm, its conformance to pits andprojections on the surface of an object to be laminated is liable todeteriorate.

Illustrative examples of the above first film include polyesters such asa polyethylene terephthalate and polymer films having heat resistanceand solvent resistance such as a polypropylene and a polyethylene.

Further, the photosensitive layer in the photosensitive film for circuitformation in the present invention has a thickness of 0.1 to 10 μm,preferably 1 to 8 μm, and more preferably 3 to 7 μm, from the viewpointsof increases in density and resolution of printed wiring.

Further, when containing a2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane, the photosensitivelayer in the photosensitive film for circuit formation in the presentinvention has a thickness of 0.1 to 14 μm, preferably 0.1 to 10 μm, morepreferably 1 to 10 μm, much more preferably 2 to 8 μm, and particularlypreferably 3 to 7 μm, from the viewpoints of increases in density andresolution of printed wiring.

The above 2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane is notparticularly limited but is preferably a compound represented by thefollowing general formula (I), for example.

In the above general formula (I), R¹ and R² each independently representa hydrogen atom or a methyl group and are preferably a methyl group.Further, in the above general formula (I), X¹ and X² each independentlyrepresent an alkylene group having 2 to 6 carbon atoms and arepreferably an ethylene group or propylene group, and particularlypreferably an ethylene group. In the above general formula (I), p and qare positive integers selected such that p+q=4 to 40. p+q is preferably6 to 34, more preferably 8 to 30, much more preferably 8 to 28,particularly preferably 8 to 20, extremely preferably 8 to 16 and mostpreferably 8 to 12. When p+q is smaller than 4, compatibility with abinder polymer (A) which is a constituent of the photosensitive layerdeteriorates, so that the photosensitive film is liable to come off whenlaminated on a substrate intended for circuit formation. On the otherhand, when p+q is larger than 40, hydrophilicity increases, so that aresist image is liable to come off at the time of development, andresistance to plating, such as solder plating, is also liable todeteriorate.

Illustrative examples of the above alkylene group having 2 to 6 carbonatoms include an ethylene group, a propylene group, an isopropylenegroup, a butylene group, a pentylene group, a hexylene group, and theirstructural isomers. From the viewpoints of resolution and resistance toplating, the alkylene group is preferably an ethylene group or anisopropylene group and is particularly preferably an ethylene group.

Further, aromatic rings in the above general formula (I) may havesubstituents. Illustrative examples of such substituents include halogenatoms, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl grouphaving 3 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms,a phenacyl group, an amino group, an alkylamino group having 1 to 10carbon atoms, a dialkylamino group having 2 to 20 carbon atoms, a nitrogroup, a cyano group, a carbonyl group, a mercapto group, analkylmercapto group having 1 to 10 carbon atoms, an allyl group, ahydroxyl group, a hydroxyalkyl group having 1 to 20 carbon atoms, acarboxyl group, a carboxyalkyl group having an alkyl group having 1 to10 carbon atoms, an acyl group having an alkyl group having 1 to 10carbon atoms, an alkoxy group having 1 to 20 carbon atoms, analkoxycarbonyl group having 1 to 20 carbon atoms, an acyloxy grouphaving 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbonatoms, an N-alkylcarbamoyl group having 2 to 10 carbon atoms or a grouphaving a heterocyclic ring, and aryl groups substituted by thesesubstituents. The above substituents may form a condensed ring. Further,hydrogen atoms in these substituents may be substituted by the abovesubstituents such as halogen atoms. In addition, when each of thearomatic rings is substituted by two or more substituents, these two ormore substituents may be the same or different.

Illustrative examples of the compound represented by the above generalformula (I) include bisphenol-A-based (meth)acrylate compounds such as a2,2-bis(4-((meth)acryloxypolyethoxy)phenyl)propane, a2,2-bis(4-((meth)acryloxypolypropoxy)phenyl)propane, a2,2-bis(4-((meth)acryloxypolybutoxy)phenyl)propane and a2,2-bis(4-((meth)acryloxypolyethoxypolypropoxy)phenyl) propane.

Specific examples of the above2,2-bis(4-((meth)acryloxypolyethoxy)phenyl)propane include2,2-bis(4-((meth)acryloxydiethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytriethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytetraethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypentaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyhexaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyheptaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyoctaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxynonaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxydecaethoxy)phenyl),2,2-bis(4-((meth)acryloxyundecaethoxy)phenyl),2,2-bis(4-((meth)acryloxydodecaethoxy)phenyl),2,2-bis(4-((meth)acryloxytridecaethoxy)phenyl),2,2-bis(4-((meth)acryloxytetradecaethoxy)phenyl),2,2-bis(4-((meth)acryloxypentadecaethoxy)phenyl), and2,2-bis(4-((meth)acryloxyhexadecaethoxy)phenyl). These may be used aloneor in a combination of two or more.

Of such compounds, for example,2,2-bis(4-((methacryloxypentaethoxy)phenyl)propane is commerciallyavailable as BPE-500 (product of Shin-Nakamura Chemical Co., Ltd.,product name), and 2,2-bis(4-((methacryloxypentadecaethoxy)phenyl) iscommercially available as BPE-1300 (product of Shin-Nakamura ChemicalCo., Ltd., product name).

Specific examples of the above2,2-bis(4-((meth)acryloxypolypropoxy)phenyl)propane include2,2-bis(4-((meth)acryloxydipropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytripropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytetrapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypentapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyhexapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyheptapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyoctapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxynonapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxydecapropoxy)phenyl),2,2-bis(4-((meth)acryloxyundecapropoxy)phenyl),2,2-bis(4-((meth)acryloxydodecapropoxy)phenyl),2,2-bis(4-((meth)acryloxytridecapropoxy)phenyl),2,2-bis(4-((meth)acryloxytetradecapropoxy)phenyl),2,2-bis(4-((meth)acryloxypentadecapropoxy)phenyl), and2,2-bis(4-((meth)acryloxyhexadecapropoxy)phenyl). These may be usedalone or in a combination of two or more.

Illustrative examples of the above2,2-bis(4-((meth)acryloxypolyethoxypolypropoxy)phenyl)propane include2,2-bis(4-((meth)acryloxydiethoxyoctapropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytetraethoxytetrapropoxy)phenyl) propane, and2,2-bis(4-((meth)acryloxyhexaethoxyhexapropoxy)phenyl)propane. These maybe used alone or in a combination of two or more.

The cushion layer in the present invention is composed mainly of acopolymer containing ethylene as an essential copolymerizable component.Illustrative examples of the copolymer include an EVA (ethylene/vinylacetate copolymer) and an EEA (ethylene/ethyl acrylate copolymer). Thecontent of copolymerized ethylene in the EVA or EEA is preferably 60 to90 wt %, more preferably 60 to 80 wt %, and much more preferably 65 to80 wt %. When the content of the copolymerized ethylene is lower than 60wt %, adhesion of the cushion layer becomes high, and adhesion betweenthe cushion layer and the photosensitive layer also becomes high, sothat it is seen that peeling of the cushion layer is liable to becomedifficult. On the other hand, when the content of the copolymerizedethylene is higher than 90 wt %, adhesion between the cushion layer andthe photosensitive layer becomes low, so that the cushion layer isliable to come off the photosensitive layer, and preparation of aphotosensitive film for circuit formation which includes the cushionlayer is liable to become difficult.

As for the relationship of interlayer adhesion among the cushion layer,the first film and the photosensitive layer, interlayer adhesion betweenthe first film and the cushion layer is preferably higher than thatbetween the cushion layer and the photosensitive layer. Thereby, thecushion layer can be peeled from the photosensitive layer.

The layer thickness of the above cushion layer is preferably 1 to 100μm, more preferably 10 to 50 μm, and much more preferably 15 to 40 μm.When the layer thickness is 1 μm or smaller, conformance to pits andprojections on the surface of an object to be laminated is liable tolower, while when the layer thickness is larger than 100 μm, costs areliable to increase. Further, it is also possible to prevent migration ofthe component (B) or (C) from the photosensitive layer to the cushionlayer by incorporating the above component (A), (B) or (C) into thecushion layer in an amount that does not impair the effect of thepresent invention.

The second film in the present invention is used as a protective filmand is removed prior to lamination. A film that can be used as thesecond film is not particularly limited as long as it has flexibility,can be removably adhered to the photosensitive layer and is not damagedby a temperature in a drying oven. Illustrative examples of such asecond film include paper, mold release paper, a polyester film such asa polyethylene terephthalate, a polyolefin film such as apolymethylpentene, a polypropylene or a polyethylene, ahalogen-containing vinyl polymer film such as a polyvinyl fluoride or apolyvinyl chloride, a polyamide film such as a nylon, a cellulose filmsuch as a cellophane, and a polystyrene film. These may be transparentor opaque and may have undergone mold release treatment.

Illustrative examples of second films which are available include E-200Hwhich is a product of Oji Paper Co., Ltd. and NF-13 which is a productof TAMAPOLY CO., LTD.

The thickness of the second film in the present invention is notparticularly limited. However, in consideration of the size of thephotosensitive film of the present invention when rolled up, thethickness of the second film is preferably 5 to 200 μm, more preferably10 to 100 μm and particularly preferably 10 to 50 μm.

Further, interlayer adhesion between the second film and thephotosensitive layer is preferably lower than that between the cushionlayer and the photosensitive layer. Thereby, the second film can bepeeled from the photosensitive layer.

In short, it is preferable that adhesion (α) between the second film andthe photosensitive layer be lower than adhesion (β) between the firstfilm and the photosensitive layer, adhesion (γ) between the first filmand the cushion layer and adhesion (δ) between the cushion layer and thephotosensitive layer, in order that the second layer can be peeledeasily so as to form a transfer layer.

In other words, it is preferable that the adhesion (β) between the firstfilm and the photosensitive layer, the adhesion (γ) between the firstfilm and the cushion layer and the adhesion (δ) between the cushionlayer and the photosensitive layer be higher than the adhesion (α)between the second film and the photosensitive layer at 180° peelstrength. Otherwise, there is no particular limitation.

Further, the photosensitive film for circuit formation of the presentinvention may have an intermediate layer(s) and/or a protective layer(s)such as an adhesive layer, a light absorbing layer and a gas barrierlayer in addition to the first film, the photosensitive layer, and thecushion layer and the second film which are used as required.

The photosensitive film for circuit formation of the present inventionwhich has the above-described lamination structure can be stored in arolled form.

The photosensitive layer of the present invention comprises (A) a binderpolymer, (B) a photopolymerizable compound having at least onepolymerizable ethylenically unsaturated bond, and (C) aphotopolymerization initiator.

The binder polymer (A) which is a component contained in thephotosensitive layer of the present invention is not particularlylimited. Illustrative examples thereof include an acrylic resin, astyrene resin, an epoxy resin, an amido resin, an amidoepoxy resin, analkyd resin, and a phenol resin. From the viewpoint of alkalidevelopability, an acrylic resin is preferred. These can be used aloneor in a combination of two or more.

Such binder polymers as an acrylic resin and a styrene resin can beproduced by, for example, radical polymerization of polymerizablemonomers. Illustrative examples of the above polymerizable monomersinclude styrene, polymerizable styrene derivatives having a substituentat an α position or in an aromatic ring such as vinyl toluene andα-methylstyrene, acrylamide such as diacetone acrylamide, esters ofvinyl alcohol such as acrylonitrile and vinyl-n-butyl ether, alkyl(meth)acrylates, tetrahydrofurfuryl (meth)acrylate, dimethylaminoethyl(meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl(meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate,2,2,3,3-tetrafluoropropyl (meth)acrylate, (meth)acrylic acid,α-bromo(meth)acrylic acid, α-chlor(meth)acrylic acid,β-furyl(meth)acrylic acid, β-styryl(meth)acrylic acid, maleic acid,maleic anhydride, maleic monoesters such as monomethyl maleate,monoethyl maleate and monoisopropyl maleate, fumaric acid, cinnamicacid, α-cyanocinnamic acid, itaconic acid, crotonic acid, and propiolicacid. Illustrative examples of the above alkyl (meth)acrylates includecompounds represented by a general formula (II):

(wherein R³ represents a hydrogen atom or a methyl group, and R⁴represents an alkyl group having 1 to 12 carbon atoms),

and compounds obtained by bonding a hydroxyl group, an epoxy group, ahalogen group or the like to the alkyl groups of these compounds.

Illustrative examples of the C₁ to C₁₂ alkyl group represented by R⁴ inthe above general formula (II) include a methyl group, an ethyl group, apropyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group, a nonyl group, a decyl group, an undecyl group, adodecyl group, and their structural isomers. Illustrative examples ofmonomers represented by the above general formula (II) include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl(meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl(meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, anddodecyl (meth)acrylate. These can be used alone or in a combination oftwo or more.

Further, the binder polymer which is the component (A) in the presentinvention preferably contains a carboxyl group from the viewpoint ofalkali developability. The binder polymer can be produced by radicalpolymerization of a polymerizable monomer having a carboxyl group withother polymerizable monomer. As the polymerizable monomer having acarboxyl group, methacrylic acid, acrylic acid and maleic acid arepreferred.

The acid value of such a binder polymer (A) is preferably 100 to 500mgKOH/g, more preferably 100 to 300 mgKOH/g. When the acid value issmaller than 100 mgKOH/g, development is liable to take a long time,while when the acid value is larger than 500 mgKOH/g, the resistance todeveloper of a photo-cured resist is liable to deteriorate.

Further, the binder polymer which is the component (A) in the presentinvention preferably contains styrene or a styrene derivative as apolymerizable monomer from the viewpoint of flexibility. The styrenederivative may be the aforementioned α-methylstyrene. To have goodadhesion and peelability, styrene or the styrene derivative as acopolymerizable component is preferably contained in an amount of 0.1 to30 wt %, more preferably 1 to 28 wt %, and particularly preferably 1.5to 27 wt %. When the content is lower than 0.1 wt %, adhesion is liableto be poor, while when the content is higher than 30 wt %, a piece to bepeeled becomes large, and peeling is liable to take a long time.

The weight average molecular weight of such a binder polymer (A) ispreferably 20,000 to 300,000 and more preferably 40,000 to 150,000. Whenthe weight average molecular weight is lower than 20,000, resistance todeveloper is liable to deteriorate, while when it is higher than300,000, development time is liable to become long. The weight averagemolecular weight in the present invention is a value measured by gelpermeation chromatography and expressed in terms of standardpolystyrene.

The above-described binder polymers (A) are used alone or in acombination of two or more. Illustrative examples of binder polymerswhich are used in a combination of two or more include two or morebinder polymers comprising different copolymerizable components, two ormore binder polymers having different weight average molecular weights,and two or more binder polymers having different degrees of dispersion.Further, the binder polymer may incorporate a photosensitive group asrequired so as to be used as a polymer having a photosensitive group.

As the photopolymerizable compound (B) having at least one polymerizableethylenically unsaturated bond which is a component contained in thephotosensitive layer of the present invention, a variety ofphotopolymerizable compounds can be used in addition to the foregoing2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane. Illustrativeexamples of these photopolymerizable compounds include compoundsobtained by reacting a polyhydric alcohol with an α,β-unsaturatedcarboxylic acid, compounds obtained by reacting aglycidyl-group-containing compound with an α,β-unsaturated carboxylicacid, an urethane (meth)acryl monomer, nonylphenyldioxylene(meth)acrylate,γ-chloro-β-hydroxypropyl-β′-(meth)acryloyloxyethyl-o-phthalate,β-hydroxyethyl-β′-(meth)acryloyloxyethyl-o-phthalate,β-hydroxypropyl-β′-(meth)acryloyloxyethyl-o-phthalate, and alkyl(meth)acrylates.

Illustrative examples of the above compounds obtained by reacting apolyhydric alcohol with an α,β-unsaturated carboxylic acid includepolyethylene glycol di(meth)acrylate having 2 to 14 ethylene groups,polypropylene glycol di(meth)acrylate having 2 to 14 propylene groups,trimethylolpropane di(meth)acrylate, trimethylolpropanetri(meth)acrylate, trimethylolpropane ethoxy tri(meth)acrylate,trimethylolpropane diethoxy tri(meth)acrylate, trimethylolpropanetriethoxy tri(meth)acrylate, trimethylolpropane tetraethoxytri(meth)acrylate, trimethylolpropane pentaethoxy tri(meth)acrylate,tetramethylolmethane tri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, anddipentaerythritol hexa(meth)acrylate. Illustrative examples of theα,β-unsaturated carboxylic acid include (meth)acrylic acid.

Illustrative examples of the above glycidyl-group-containing compoundinclude trimethylolpropane triglycidyl ether tri(meth)acrylate, and2,2-bis(4-(meth)acryloxy-2-hydroxy-propyloxy)benzene.

Illustrative examples of the above urethane (meth)acryl monomer includeaddition reaction products of a (meth)acryl monomer having an —OH groupat a β position with isophorone diisocyanate, 2,6-toluene diisocyanate,2,4-toluene diisocyanate and 1,6-hexamethylene diisocyanate,tris((meth)acryloxytetraethylene glycol isocyanate)hexamethyleneisocyanurate, EO-modified urethane di(meth)acrylate, and EO.PO-modifiedurethane di(meth)acrylate. EO represents ethylene oxide, and anEO-modified compound has a block structure of an ethylene oxide group.Further, PO represents propylene oxide, and a PO-modified compound has ablock structure of a propylene oxide group.

Illustrative examples of the above alkyl (meth)acrylates include methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and2-ethylhexyl (meth)acrylate.

These photopolymerizable compounds including the2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane are used alone or ina combination of two or more.

Illustrative examples of the photopolymerization initiator (C) which isa component of the photosensitive layer in the present invention includearomatic ketones such as benzophenone,N,N′-tetramethyl-4,4′-diaminobenzophenone (Michler's ketone),N,N′-tetraethyl-4,4′-diaminobenzophenone,4-methoxy-4′-dimethylaminobenzophenone,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propanone-1, quinonessuch as 2-ethylanthraquinone, phenanthrenequinone,2-t-butylanthraquinone, octamethylanthraquinone, 1,2-benzanthraquinone,2,3-benzanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone,1-chloroanthraquinone, 2-methylanthraquinone, 1,4-naphthoquinone,9,10-phenanthraquinone, 2-methyll,4-naphthoquinone, and2,3-dimethylanthraquinone, benzoin ether compounds such as benzoinmethyl ether, benzoin ethyl ether, and benzoin phenyl ether, benzoincompounds such as benzoin, methyl benzoin, and ethyl benzoin, benzylderivatives such as benzyl dimethyl ketal, 2,4,5-triarylimidazole dimerssuch as a 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer, a2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazole dimer, a2-(o-fluorophenyl)-4,5-diphenylimidazole dimer, a2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer, and a2-(p-methoxyphenyl)-4,5-diphenylimidazole dimer, acridine derivativessuch as 9-phenylacridine and 1,7-bis(9,9′-acridinyl)heptane,N-phenylglycine, N-phenylglycine derivatives, and cumarine-basedcompounds. As substituents of the aryl groups of the two2,4,5-triarylimidazoles, identical, symmetrical compounds or different,asymmetrical compounds may be provided. Further, as exemplified by acombination of diethylthioxanthone and dimethylaminobenzoic acid, athioxanthone-based compound and a tertiary amine compound may becombined. In addition, from the viewpoints of adhesion and sensitivity,a 2,4,5-triarylimidazole dimer is more preferable. These are used aloneor in a combination of two or more.

As for the amounts of the components in the photosensitive layer, theamount of the binder polymer (A) is preferably 40 to 80 parts by weight,more preferably 45 to 70 parts by weight, based on 100 parts by weightof the total amount of the components (A) and (B). When the amount issmaller than 40 parts by weight, a photo-cured product is liable tobecome brittle, and the film is liable to have poor coatability whenused as a photosensitive element, while when it is larger than 80 partsby weight, light sensitivity is liable to be insufficient.

The amount of the foregoing photopolymerizable compound (B) having atleast one polymerizable ethylenically unsaturated bond is preferably 20to 60 parts by weight, more preferably 30 to 55 parts by weight, basedon 100 parts by weight of the total amount of the components (A) and(B). When the amount is smaller than 20 parts by weight, lightsensitivity is liable to be insufficient, while when it is larger than60 parts by weight, a photo-cured product is liable to become brittle.

The amount of the foregoing photopolymerization initiator (C) ispreferably 0.1 to 20 parts by weight, more preferably 0.2 to 10 parts byweight, based on 100 parts by weight of the total amount of thecomponents (A) and (B). When the amount is smaller than 0.1 parts byweight, light sensitivity is liable to be insufficient, while when it islarger than 20 parts by weight, absorption on the surface of acomposition increases at the time of exposure, so that photo-curing ofthe inside of the composition is liable to be insufficient.

Further, the photosensitive layer may contain a dye such as malachitegreen, a photo-coupler such as tribromophenylsulfone or leuco crystalviolet, a thermal color development inhibitor, a plasticizer such asp-toluenesulfoneamide, a pigment, a filler, an antifoaming agent, aflame retardant, a stabilizer, an adhesion imparting agent, a levelingagent, a peeling promoter, an antioxidant, a perfume, an imaging agent,and a thermal crosslinking agent as required. These additives each maybe added in an amount of about 0.01 to 20 parts by weight based on 100parts by weight of the total amount of the components (A) and (B). Theseadditives are used alone, or in a combination of two or more asrequired.

To form the photosensitive layer on the first film or cushion layer, aphotosensitive resin composition prepared by compounding the components(A), (B) and (C) and, as required, the above additives is applied. Uponapplication, the photosensitive resin composition can be dissolved in asolvent as required, so as to be applied as a solution having a solidcontent of about 30 to 60 wt %. Illustrative examples of the solventinclude methanol, ethanol, acetone, methyl ethyl ketone, methylcellosolve, ethyl cellosolve, toluene, N,N-dimethylformamide, andpropylene glycol monomethyl ether. These may be used alone or in acombination of two or more.

Such a photosensitive layer preferably has a transmittance of 5 to 75%,more preferably 7 to 60%, and particularly preferably 10 to 40%, withrespect to ultraviolet radiation having a wavelength of 365 nm. When thetransmittance is lower than 5%, adhesion is liable to be poor, whilewhen it is higher than 75%, resolution is liable to be poor. The abovetransmittance can be measured by means of an UV spectrometer. An exampleof the above UV spectrometer is a W beam spectrophotometer 228A ofHITACHI LTD.

The method of the present invention for producing a printed wiring boardis exemplified by a method in which after the second film, if present,is removed, the photosensitive layer is crimped on a substrate forcircuit formation under heat so as to be laminated on the substrate. Thelamination is preferably carried out under a reduced pressure from theviewpoints of adhesion and conformance. A surface to be laminated isgenerally a metallic surface but is not particularly limited. Theheating temperature of the photosensitive layer is preferably 70 to 130°C., and a crimping pressure is preferably about 0.1 to 1.0 MPa (about 1to 10 kgf/cm²). These conditions, however, are not particularly limited.Further, although preheating of the substrate for circuit formation isnot required if the photosensitive layer is heated at 70 to 130° C. asdescribed above, the substrate for circuit formation may be preheated soas to further improve laminatability.

The thus laminated photosensitive layer is irradiated with activationradiation image-wise through a negative or positive mask pattern calledan artwork. In this case, when the first film or cushion layer presenton the photosensitive layer is transparent, the activation radiation maybe irradiated either directly or after removal of the first film or thecushion layer. However, when the first film or the cushion layer isopaque, the activation radiation must be irradiated after removal of thefilm or the layer. As a light source of the activation radiation, aknown light source capable of effective irradiation of ultravioletradiation such as a carbon arc lamp, a mercury vapor arc lamp, a superhigh pressure mercury lamp, a high pressure mercury lamp or a xenon lampis used. In addition, a light source capable of effective radiation ofvisible radiation such as a floodlight for photographs or a sunlamp isalso used.

Then, after exposure to the radiation, when the first film or cushionlayer is present on the photosensitive layer, the first film or cushionlayer is removed first, and unexposed portions are then removed by wetdevelopment, dry development or other means so as to produce a resistpattern. In the wet development, a developer suited for thephotosensitive resin composition, such as an alkaline aqueous solution,a water-based developer or an organic solvent, is used, and developmentis carried out by a known method such as spraying, fluctuationimmersion, brushing or scraping. As for the developer, one which is,safe stable and easy to use such as an alkaline aqueous solution isused.

As a base of the above alkaline aqueous solution, a hydroxide of analkali metal such as lithium hydroxide, sodium hydroxide or potassiumhydroxide, a carbonate such as lithium carbonate, sodium carbonate,potassium carbonate, ammonium carbonate, lithium hydrogen carbonate,sodium hydrogen carbonate, potassium hydrogen carbonate or ammoniumhydrogen carbonate, a phosphate of an alkali metal such as potassiumphosphate or sodium phosphate, or a pyrophosphate of an alkali metalsuch as sodium pyrophosphate or potassium pyrophosphate is used.Further, as the alkaline aqueous solution used in the development, adilute solution containing 0.1 to 5 wt % of sodium carbonate, a dilutesolution containing 0.1 to 5 wt % of potassium carbonate, a dilutesolution containing 0.1 to 5 wt % of sodium hydroxide, a dilute solutioncontaining 0.1 to 5 wt % of sodium tetraborate, or the like ispreferred.

Further, the alkaline aqueous solution used in the developmentpreferably has a pH of 9 to 11. Its temperature is adjusted according tothe developability of the photosensitive layer and is generally about 25to 35° C. Further, in the alkaline aqueous solution, a surfactant, anantifoaming agent, a small amount of organic solvent for acceleratingthe development, and other additives may be contained.

The above water-based developer comprises water or an alkaline aqueoussolution, and at least one organic solvent. Illustrative examples ofalkali materials in this case include borax, sodium metasilicate,tetramethylammonium hydroxide, ethanolamine, ethylenediamine,diethylenetriamine, 2-amino-2-hydroxymethyl-1,3-propanediol,1,3-diaminopropanol-2, and morpholine, in addition to the foregoingmaterials. The pH of the developer is preferably as low as possiblewithin a range in which the resist can be developed to a sufficientdegree. The pH is preferably 8 to 12, more preferably 9 to 10.Illustrative examples of the above organic solvent include triacetonealcohol, acetone, ethyl acetate, an alkoxy ethanol having an alkoxygroup having 1 to 4 carbon atoms, ethyl alcohol, isopropyl alcohol,butyl alcohol, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, and diethylene glycol monobutyl ether. These are usedalone or in a combination of two or more. In general, the concentrationof the organic solvent is preferably 2 to 90 wt %, and its temperaturecan be adjusted according to developability. Further, in the water-baseddeveloper, a small amount of surfactant, antifoaming agent or the likecan be contained.

Illustrative examples of an organic-solvent-based developer which isused alone include 1,1,1-trichloroethane, N-methylpyrrolidone,N,N-dimethylformamide, cyclohexanone, methyl isobutyl ketone, andγ-butyrolactone. These organic solvents preferably contain water in anamount of 1 to 20 wt % so as to prevent catching fire.

Further, as required, two or more development methods can be used in acombination. Illustrative examples of the development methods includedipping, battling, spraying, brushing, and slapping. Of these,high-pressure spraying is the most suitable for improving resolution.

As post-development treatment, the resist pattern may be heated at about60 to 250° C. or exposed to about 0.2 to 10 mJ/cm² as required so as tobe further cured before use.

To etch a metallic surface after development, a cupric chloridesolution, a ferric chloride solution, an alkali etching solution or ahydrogen-peroxide-based etching solution can be used. However, from theviewpoint of good etch-factor, it is desirable to use a ferric chloridesolution.

When a printed wiring board is produced by use of the photosensitivefilm for circuit formation of the present invention, the surface of asubstrate for circuit formation is treated by a known method such asetching or plating by use of a developed resist pattern as a mask.Illustrative examples of the above plating include copper plating suchas copper sulfate plating and copper pyrophosphate plating, solderplating such as high-slow plating, nickel plating such as watt bath(nickel sulfate-nickel chloride) and nickel sulfamate plating, and goldplating such as hard gold plating and soft gold plating. Then, theresist pattern can be removed by use of, for example, a strongeralkaline aqueous solution than an alkaline aqueous solution used indevelopment. As for the stronger alkaline aqueous solution, an aqueoussolution containing 1 to 10 wt % of sodium hydroxide, an aqueoussolution containing 1 to 10 wt % of potassium hydroxide or otheralkaline aqueous solution is used, for example.

Illustrative examples of a method to remove the resist pattern includeimmersion and spraying. Immersion and spraying may be used alone or incombination. Further, a printed wiring board having the resist patternformed thereon may be a multilayer printed wiring board.

Hereinafter, the present invention will be described in more detail withreference to Examples. However, the present invention shall not belimited to these Examples.

EXAMPLES 1 TO 8 AND COMPARATIVE EXAMPLES 1 TO 6

[Preparation of Photosensitive Layer Material]

Materials shown in Table 1 were compounded to prepare a solution of aphotosensitive layer material (I).

TABLE 1 Item Material Amount Component (A) 40-wt % Methylcellosolve/toluene 137.5 parts by weight (weight ratio: 60/40) solutionof (solid content: 55 methacrylic acid/methyl methacrylate/styrene partsby weight) copolymer (weight ratio: 20/60/20, weight average molecularweight: 60,000) Component (B) 2,2′-Bis((4- 30 parts by weightmethacryloxypentaethoxy) phenyl)propane Υ-Chloro-β-hydroxypropyl-β′- 15parts by weight methacryloyloxyethyl-ophthalate Component (C)2-(o-Chlorophenyl)-4,5-diphenylimidazole dimer 3.0 parts by weight4,4′-Bisdiethylaminobenzophenone 0.2 parts by weight Color DeveloperLeuco crystal violet 0.5 parts by weight Dye Malachite green 0.05 partsby weight Solvent Acetone 10 parts by weight Toluene 10 parts by weightMethanol 3 parts by weight N,N-Dimethylformamide 3 parts by weight[Preparation of Cushion Layer Materials]

Materials shown in Table 2 were compounded to prepare solutions ofcushion layer materials (I), (II) and (III).

TABLE 2 Ethylene Amount Component (parts by Item Material (wt %) weight)Cushion Toluene — 83 Layer EVAFLEX EEA709 65 17 (I) (DU PONT-MITSUIPOLYCHEMICALS CO., LTD.) Cushion Toluene — 83 Layer EVAFLEX EV45X 54 17(II) (DU PONT-MITSUI POLYCHEMICALS CO., LTD.) Cushion Toluene — 83 LayerEVAFLEX EEA701 91 17 (III) (DU PONT-MITSUI POLYCHEMICALS CO., LTD.)

Example 1

[Preparation of Photosensitive Film (1) for Circuit Formation]

On a 16-μm-thick polyethylene terephthalate film (trade name: G2-16,product of TEIJIN LTD.) as a first film, the solution of thephotosensitive layer material (I) was applied uniformly such that thematerial (I) would have a thickness of 4 μm after drying, and theapplied solution was dried by means of a hot air convection-type dryerat 100° C. for 10 minutes. Thereafter, the photosensitive layer wasprotected by a 20-μm-thick biaxially stretched polypropylene film (tradename: E-200H, a product of Oji Paper Co., Ltd.) as a second film so asto obtain a photosensitive film (1) for circuit formation. The obtainedphotosensitive film (1) for circuit formation was rolled up with thefirst film exposed to the outside.

Example 2

[Preparation of Photosensitive Film (2) for Circuit Formation]

A photosensitive film (2) for circuit formation was prepared in the samemanner as in Example 1 except that the thickness of the photosensitivelayer after drying was changed to 6 μm. The obtained photosensitive film(2) for circuit formation was rolled up with the first film exposed tothe outside.

Example 3

[Preparation of Photosensitive Film (3) for Circuit Formation]

On a 16-μm-thick polyethylene terephthalate film (trade name: G2-16,product of TEIJIN LTD.) as a first film, the solution of the cushionlayer material (I) was applied uniformly such that the material (I)would have a thickness of 10 μm after drying, and the applied solutionwas dried by means of a hot air convection-type dryer at 100° C. for 10minutes. Then, on the cushion layer, the solution of the photosensitivelayer material (I) was applied uniformly such that the material (I)would have a thickness of 4 μm after drying, and the applied solutionwas dried by means of a hot air convection-type dryer at 100° C. for 10minutes. Thereafter, the photosensitive layer was protected by a20-μm-thick biaxially stretched polypropylene film (trade name: E-200H,a product of Oji Paper Co., Ltd.) as a second film so as to obtain aphotosensitive film (3) for circuit formation. The obtainedphotosensitive film (3) for circuit formation was rolled up with thefirst film exposed to the outside.

Example 4

[Preparation of Photosensitive Film (4) for Circuit Formation]

A photosensitive film (4) for circuit formation was prepared in the samemanner as in Example 3 except that the thickness of the photosensitivelayer after drying was changed to 6 μm. The obtained photosensitive film(4) for circuit formation was rolled up with the first film exposed tothe outside.

Example 5

[Preparation of Photosensitive Film (5) for Circuit Formation]

A photosensitive film (5) for circuit formation was prepared in the samemanner as in Example 3 except that the thickness of the cushion layerafter drying was changed to 20 μm. The obtained photosensitive film (5)for circuit formation was rolled up with the first film exposed to theoutside.

Example 6

[Preparation of Photosensitive Film (6) for Circuit Formation]

A photosensitive film (6) for circuit formation was prepared in the samemanner as in Example 3 except that the thickness of the photosensitivelayer after drying was changed to 6 μm and the thickness of the cushionlayer after drying was changed to 20 μm. The obtained photosensitivefilm (6) for circuit formation was rolled up with the first film exposedto the outside.

Example 7

[Preparation of Photosensitive Film (7) for Circuit Formation]

A photosensitive film (7) for circuit formation was prepared in the samemanner as in Example 3 except that the thickness of the cushion layerafter drying was changed to 30 μm. The obtained photosensitive film (7)for circuit formation was rolled up with the first film exposed to theoutside.

Example 8

[Preparation of Photosensitive Film (8) for Circuit Formation]

A photosensitive film (8) for circuit formation was prepared in the samemanner as in Example 3 except that the thickness of the photosensitivelayer after drying was changed to 6 μm and the thickness of the cushionlayer after drying was changed to 30 μm. The obtained photosensitivefilm (8) for circuit formation was rolled up with the first film exposedto the outside.

Comparative Example 1

[Preparation of Photosensitive Film (9) for Circuit Formation]

A photosensitive film (9) for circuit formation was prepared in the samemanner as in Example 1 except that the thickness of the photosensitivelayer after drying was changed to 20 μm. The obtained photosensitivefilm (9) for circuit formation was rolled up with the first film exposedto the outside.

Comparative Example 2

[Preparation of Photosensitive Film (10) for Circuit Formation]

A photosensitive film (10) for circuit formation was prepared in thesame manner as in Example 3 except that the thickness of thephotosensitive layer after drying was changed to 20 μm. The obtainedphotosensitive film (10) for circuit formation was rolled up with thefirst film exposed to the outside.

Comparative Example 3

[Preparation of Photosensitive Film (11) for Circuit Formation]

A photosensitive film (11) for circuit formation was prepared in thesame manner as in Example 3 except that the thickness of the cushionlayer after drying was changed to 20 μm and the thickness of thephotosensitive layer after drying was changed to 20 μm. The obtainedphotosensitive film (11) for circuit formation was rolled up with thefirst film exposed to the outside.

Comparative Example 4

[Preparation of Photosensitive Film (12) for Circuit Formation]

A photosensitive film (12) for circuit formation was prepared in thesame manner as in Example 3 except that the thickness of the cushionlayer after drying was changed to 30 μm and the thickness of thephotosensitive layer after drying was changed to 20 μm. The obtainedphotosensitive film (12) for circuit formation was rolled up with thefirst film exposed to the outside.

Comparative Example 5

[Preparation of Photosensitive Film (13) for Circuit Formation]

A photosensitive film (13) for circuit formation was prepared in thesame manner as in Example 3 except that the cushion layer material (II)was used in place of the cushion layer material (I). The obtainedphotosensitive film (13) for circuit formation was rolled up with thefirst film exposed to the outside.

Comparative Example 6

[Preparation of Photosensitive Film (14) for Circuit Formation]

A photosensitive film (14) for circuit formation was prepared in thesame manner as in Example 3 except that the cushion layer material (III)was used in place of the cushion layer material (I). The obtainedphotosensitive film (14) for circuit formation was rolled up with thefirst film exposed to the outside.

Then, printed wiring boards were prepared in the following manner.

[Preparation of Printed Wiring Board A]

A copper foil having a thickness of 35 μm laminated on glass epoxysubstrates (product of HITACHI CHEMICAL CO., LTD., trade name:MCL-E67-³⁵S) was grounded by means of a grinder (product of SANKEI CO.,LTD.) having a #600-equivalent brush, rinsed, and then dried by an aircurrent so as to obtain copper-clad laminates.

Then, after the obtained copper-clad laminates were heated to 80° C.,the photosensitive films (1) to (14) for circuit formation which hadbeen prepared in Examples 1 to 8 and Comparative Examples 1 to 6 werelaminated on the above substrates by use of a high-temperature laminator(product of HITACHI CHEMICAL CO., LTD., trade name: HLM-3000) whileremoving the second films from the films (1) to (14) such that thephotosensitive layers faced the substrates and the first films madecontact with a roller.

In this case, the speed of the laminate roll was 1.5 m/min, thetemperature of the laminate roll was 110° C., and the cylinder pressureof the roll was 0.4 MPa (4 kgf/cm²).

At this time, since adhesion between the photosensitive layer andcushion layer of the photosensitive film (14) for circuit formation waslower than adhesion between the second film and photosensitive layerthereof, the second film could not be peeled easily, so that the filmcould not be laminated on the copper-clad laminate.

Then, after lamination, the substrates were cooled to 23° C. Then, onthe first films, negative masks (negative mask having a Stauffer 21-steptablet and a wiring pattern having a line width/space width of 400/6 to400/47 (resolution, unit: μm)) were placed, and by use of an exposureinstrument manufactured by ORK Manufacturing CO., LTD. (model: EXM-1201,mercury short arc lamp), the films were exposed to energy whose amountwas such that the number of remaining steps in the Stauffer 21-steptablet after development would be 6.0.

Then, the first films of the photosensitive films (1), (2) and (9) forcircuit formation were peeled, and the first films and cushion layers ofthe photosensitive films (3) to (8) and (10) to (13) for circuitformation were peeled.

At this time, when the first film and the cushion layer were peeled fromthe photosensitive film (13) for circuit formation, its photosensitivelayer was also peeled, together with the cushion layer.

Then, by use of a 1-wt % sodium carbonate aqueous solution (30° C.), thephotosensitive films (1), (3), (5) and (7) for circuit formation werespray-developed for 4 seconds (spraying pressure: 0.18 MPa (1.8kgf/cm²)), the photosensitive films (2), (4), (6) and (8) for circuitformation were spray-developed for 6 seconds, and the photosensitivefilms (9) to (12) for circuit formation were spray-developed for 30seconds, so as to form resist patterns on the substrates. The value of aminimum space width free from undeveloped portions was measured asresolution. The results are shown in Table 3. The smaller the value, thebetter the resolution.

Then, a cupric chloride etching solution (2 mol/liter CuCl₂, 2N—HClaqueous solution, 50° C., spraying pressure: 0.2 MPa (2 kgf/cm²)) wassprayed for 100 seconds so as to dissolve copper in portions which werenot protected by the resist. Thereafter, the resist patterns wereremoved with a remover (3-wt % NaOH aqueous solution, 45° C., sprayingpressure: 0.2 MPa (2 kgf/cm²)) so as to prepare printed wiring boards Ahaving copper lines formed on the substrates.

[Preparation of Printed Wiring Board B]

After substrates were laminated in accordance with the same procedure asused in preparation of the printed wiring boards A, the first films ofthe photosensitive films (1), (2) and (9) for circuit formation werepeeled, and the first films and cushion layers of the photosensitivefilms (3) to (8) and (10) to (12) for circuit formation were peeled.Then, on the photosensitive layers, negative masks (negative mask havinga Stauffer 21-step tablet and a wiring pattern having a line width/spacewidth of 400/6 to 400/47 (resolution, unit: μm)) were placed, and by useof an exposure instrument manufactured by ORK Manufacturing CO., LTD.(model: EXM-1201, mercury short arc lamp), the films were exposed toenergy whose amount was such that the number of remaining steps in theStauffer 21-step tablet after development would be 6.0. Then,development, etching and removal steps were carried out in accordancewith the same procedure as used in preparation of the printed wiringboards A so as to prepare printed wiring boards B having copper linesformed on the substrates. The printed wiring boards B were evaluated inthe same manner as the printed wiring boards A were evaluated.

Printed wiring boards B using the photosensitive films (13) and (14) forcircuit formation could not be prepared due to the same reason as thatin preparation of the printed wiring boards A.

[Preparation of Printed Wiring Board C]

Copper-clad laminates having resist patterns formed thereon wereobtained in the same manner as in preparation of the printed wiringboards A except that a negative mask having a line width/space width of1,000 μm/100 μm was used (only the photosensitive film (5) for circuitformation was used). Then, the obtained substrates were immersed in 100g/l of ammonium persulfate aqueous solution (30° C.) for 10 minutes.Then, the resist patterns were removed with a remover (3-wt % NaOHaqueous solution, 45° C., spraying pressure: 2 kgf/cm² (0.2 MPa)) so asto obtain copper-clad laminates having a groove depth of 1 to 12 μm anda groove width of 100 μm.

Then, after the obtained copper-clad laminates were heated to 80° C.,the photosensitive films (1) to (14) for circuit formation which hadbeen prepared in Examples 1 to 8 and Comparative Examples 1 to 6 werelaminated on the above substrates by use of a high-temperature laminator(product of HITACHI CHEMICAL CO., LTD., trade name: HLM-3000) whileremoving the second films from the films (1) to (14) such that thephotosensitive layers faced the substrates and the first films madecontact with a roller (the axis of the laminate roll was parallel to thelongitudinal directions of grooves on the substrates).

In this case, the speed of the laminate roll was 1.5 m/min, thetemperature of the laminate roll was 110° C., and the cylinder pressureof the roll was 0.4 MPa (4 kgf/cm²).

Further, since adhesion between the photosensitive layer and cushionlayer of the photosensitive film (14) for circuit formation was lowerthan adhesion between the second film and photosensitive layer thereof,the second film could not be peeled easily, so that the film could notbe laminated on the copper-clad laminate.

Then, after lamination, the substrates were cooled to 23° C. Then, onthe first films, negative masks having a wiring pattern (having aStauffer 21-step tablet and a line width/space width of 100/100 (unit:μm)) were placed in a direction perpendicular to the longitudinaldirections of grooves on the substrates and brought into intimatecontact with the first films, and by use of an exposure instrumentmanufactured by ORK Manufacturing CO., LTD. (model: EXM-1201, mercuryshort arc lamp), the films were exposed to energy whose amount was suchthat the number of remaining steps in the Stauffer 21-step tablet afterdevelopment would be 6.0.

Then, the first films of the photosensitive films (1), (2) and (9) forcircuit formation were peeled, and the first films and cushion layers ofthe photosensitive films (3) to (8) and (10) to (13) for circuitformation were peeled.

At this time, when the first film and the cushion layer were peeled fromthe photosensitive film (13) for circuit formation, its photosensitivelayer was also peeled, together with the cushion layer.

Then, by use of a 1-wt % sodium carbonate aqueous solution (30° C.), thephotosensitive films (1), (3), (5) and (7) for circuit formation werespray-developed for 4 seconds (spraying pressure: 0.18 MPa (1.8kgf/cm²)), the photosensitive films (2), (4), (6) and (8) for circuitformation were spray-developed for 6 seconds, and the photosensitivefilms (9) to (12) for circuit formation were spray-developed for 30seconds, so as to form resist patterns on the substrates.

Then, a cupric chloride etching solution (2 mol/liter CuCl₂, 2N—HClaqueous solution, 50° C., spraying pressure: 0.2 MPa (2 kgf/cm²)) wassprayed for 100 seconds so as to dissolve copper in portions which werenot protected by the resist. Thereafter, the resist patterns wereremoved with a remover (3-wt % NaOH aqueous solution, 45° C., sprayingpressure: 0.2 MPa (2 kgf/cm²)) so as to prepare printed wiring boards Chaving copper lines formed on the substrates.

When the laminated film does not conform to grooves on the substrate,there is a gap between the resist and the substrate. Because of thisgap, an etching solution seeps into points where the resist and thegrooves intersect in the copper lines, thereby dissolving copper andcausing disconnection of the copper lines. The depth (μm) of the grooveat which disconnection occurs was taken as being from conformance tounevenness (the greater the value of the depth, the better theconformance). The results are shown in Table 3.

TABLE 3 Item Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 PhotosensitiveFilm (1) (2) (3) (4) (5) (6) (7) Composition of Cushion Layer — — I I II I Layer Thickness Photosensitive Layer 4 6 4 6 4 6 4 (μm) CushionLayer — — 10 10 20 20 30 Resolution Printed Wiring A 12 12 12 15 15 1820 (μm) Board B 8 10 8 10 8 10 8 Conformance to Unevenness (μm) 1 2 4 57 7 10 Comp. Comp. Comp. Comp. Comp. Comp. Item Ex. 8 Ex. 1 Ex. 2 Ex. 3Ex. 4 Ex. 5 Ex. 6 Photosensitive Film (8) (9) (10) (11) (12) (13) (14)Composition of Cushion Layer I — I I I II III Layer ThicknessPhotosensitive Layer 6 20 20 20 20 4 4 (μm) Cushion Layer 30 — 10 20 3010 10 Resolution Printed Wiring A 25 20 25 32 45 — — (μm) Board B 10 1818 18 18 — — Conformance to Unevenness (μm) 10 4 8 12 14 — —

Examples 1 and 2 using the photosensitive films (1) and (2) for circuitformation of the present invention had better resolution thanComparative Example 1 using the photosensitive film (9) for circuitformation. Further, when the resolutions of Examples 3 and 4 using thephotosensitive films (3) and (4) for circuit formation in which thedried cushion layer had a thickness of 10 μm were compared with theresolution of Comparative Example 2 using the photosensitive film (10)for circuit formation, the former had better resolutions. Similarly, asimilar tendency was observed when the thickness of the cushion layerand the thickness of the photosensitive layer were 20 μm and 30 μm.Further, Examples 3 to 8 using the photosensitive films (3) to (8) forcircuit formation in which the cushion layer was formed between thefirst film and the photosensitive layer had better conformance tounevenness than the photosensitive films (1) and (2) for circuitformation having no cushion layer. Meanwhile, in Comparative Examples 5and 6 using the photosensitive films (13) and (14) for circuitformation, print wiring boards could not be prepared.

The photosensitive films for circuit formation of the present Examplesare useful in increasing the density and resolution of printed wiringsince they can be made thin and have excellent conformance.

The photosensitive films for circuit formation of the present Examplesare flexible at the time of lamination onto a substrate, have goodconformance, and can be laminated directly by use of a conventionallaminator. Hence, there arises no problem of an increase in productioncosts caused by a change of devices or a change in steps.

The photosensitive films for circuit formation of the present Examplescan improve resolution and resist pattern accuracy, regardless of thesurface condition of a substrate, prevent disconnection or a chip in anetching step of printed wiring, improve the yield of a printed wiringboard conforming to high densification significantly, and is useful inreducing production costs.

The photosensitive films for circuit formation of the present Examplescan change adhesions among the cushion layer, the first film and thephotosensitive layer by changing the composition of a copolymercontained in the cushion layer. Therefore, the first film and thecushion layer can be peeled from the photosensitive layer easily, evenbefore exposure to light.

1. A photosensitive film for circuit formation, comprising: a firstfilm; a cushion layer comprising an ethylene/ethyl acrylate copolymerformed using ethylene as an essential copolymerizable monomer at acopolymerizing ratio of ethylene in the copolymerized monomers of 60 to90%, by weight; and a photosensitive layer having a thickness of 3 to 10μm on the first film, wherein the cushion layer is present between thefirst film and the photosensitive layer and the photosensitive layercomprises (A) a binder polymer that is a copolymer formed using astyrene or styrene derivative as an essential monomer, (B) aphotopolymerizable compound having at least one polymerizableethylenically unsaturated bond, and (C) a photopolymerization initiator;and interlayer adhesion between the first film and the cushion layer ishigher than interlayer adhesion between the cushion layer and thephotosensitive layer.
 2. The photosensitive film according to claim 1,wherein the photopolymerizable compound (B) having at least onepolymerizable ethylenically unsaturated bond includes a2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propane.
 3. Thephotosensitive film according to claim 2, wherein the binder polymer (A)contains methacrylic acid as an essential copolymerizable component. 4.The photosensitive film according to claim 2, wherein the binder polymer(A) has an acid value of 100 to 500 mgKOH/g.
 5. The photosensitive filmaccording to claim 2, wherein the binder polymer (A) has a weightaverage molecular weight of 20,000 to 300,000.
 6. The photosensitivefilm according to claim 2, wherein the binder polymer (A) containsstyrene or the styrene derivative in an amount of 0.1 to 30 wt % of allcopolymerizable components.
 7. The photosensitive film according toclaim 2, wherein the 2,2-bis(4-((meth)acryloxypolyalkoxy)phenyl)propaneis a compound represented by a general formula (I):

(wherein R¹ and R² each independently represent a hydrogen atom or amethyl group, X¹ and X² each independently represent an alkylene grouphaving 2 to 6 carbon atoms, and p and q are positive integers selectedsuch that p+q=4 to 40).
 8. The photosensitive film according to claim 7,wherein X¹ and X² are an ethylene group.
 9. The photosensitive filmaccording to claim 1, wherein the binder polymer (A) containsmethacrylic acid as an essential copolymerizable component.
 10. Thephotosensitive film according to claim 1, wherein the cushion layer hasa thickness of is 1 to 100 μm.
 11. The photosensitive film according toclaim 1, wherein a second film is present on the opposite side of a sideof the photosensitive layer on which the first film is present.
 12. Thephotosensitive film according to claim 1, wherein a second film ispresent on the opposite side of a side of the photosensitive layer onwhich the first film is present, and interlayer adhesion between thesecond film and the photosensitive layer is lower than that between thecushion layer and the photosensitive layer.
 13. A process for producinga printed wiring board, comprising the steps of: laminating thephotosensitive film for circuit formation according to claim 11 on asubstrate while peeling the second film such that the photosensitivelayer makes contact with the substrate; exposing the laminated film tolight; removing the first film or the cushion layer from thephotosensitive layer; and developing the photosensitive layer.
 14. Aprocess for producing a printed wiring board, comprising the steps of:laminating the photosensitive film for circuit formation according toclaim 11 on a substrate while peeling the second film such that thephotosensitive layer makes contact with the substrate; removing thefirst film or the cushion layer from the photosensitive layer; exposingthe photosensitive layer to light; and developing the photosensitivelayer.